Resistors have previously been made with metal housings, but have suffered from major drawbacks in critical areas. Most notably, these drawbacks are in the areas of cost, size, and power rating. Although for some limited applications cost is not a major factor, there are a great many applications where cost is of crucial importance.
Similarly, there are a great many applications where a high power rating--for a given size--is essential to commercial viability. Stated otherwise, it is extremely important that a resistor be capable of dissipating a large amount of power for its size, so that the resistor will fit into a particular space and will not become excessively hot.
For many applications it is required that the resistor be capable of withstanding large shocks and much vibration. Aerospace applications are examples of environments where shock and vibration resistance are paramount considerations. Relative to much more high-volume applications where these considerations are of major significance, reference is made to such common environments as the motor regions of vacuum cleaners and automobiles.